A clutch is provided in automobiles for interrupting transmission of the output of an engine during a shift between gear ratios of a gear transmission, and a friction clutch is most widely employed by virtue of the simple construction and the ease of maintenance. Although the friction clutch is classified into a variety of types, its basic construction is such that a release bearing is urged toward a flywheel by the clutch pedal so that a clutch disc normally pressed against the flywheel by the force of a spring can be urged away from the flywheel against the force of the spring. The clutch disc is classified into a solid type and a spring type. The spring type comprises coil springs interposed between a hub splined to the input shaft of the gear transmission and disc plates holding a friction plate making pressure engagement with the flywheel, so as to transmit torque therethrough, and is, therefore, advantageous in that a shock absorbing action is effected during engagement of the clutch.
By the way, when the engine is in its idling condition, that is, when the gear position in the transmission is neutral, "clattering" or "rattling" noise is frequently generated from the transmission. This is because, in the idling condition, a large torque variation occurs in the engine, which variation is especially marked in the case of a Diesel engine, and the resultant collision of the gears of the transmission with each other gives rise to generation of meshing noise. A structure having a special torsional characteristic is known in which, for the purpose of preventing such meshing noise, a friction washer is interposed between the disc plates and the hub so as to absorb the noise by the clutch disc. FIG. 1 shows an example of the torsional characteristic of the structure having such a function. The noise occurring during idling has concern with a first-stage hysteresis torque indicated by the symbol H.sub.1, and, for the purpose of preventing the noise, it is necessary to maintain this H.sub.1 at a certain small value suitable for the engine/transmission torsional vibration system. To this end, the co-applicant of the present application has proposed the technique of reducing the surface pressure between the disc plates and the hub and providing a plated coating for stabilizing the coefficient of friction of and improving the wear resistance of these frictional portions, in Japanese Utility Model Application No. 56-161633 laid open already as Japanese Utility Model Laid-open No. 58-67124. However, depending on the engine, this hysteresis torque H.sub.1 must be set at a very small value of the order of 0.05-0.12 kgm to avoid trouble. This is because, when the value of this hysteresis torque H.sub.1 becomes smaller than 0.05 kgm in use, the clutch disc itself makes a torsional resonance thereby generating great noise, while, when this value becomes larger than 0.12 kgm, the effect of preventing noise generated from the transmission is abruptly reduced.